The 'grep' command uses regular expressions (man regexp) so
the string *"ECU"* is not doing what you think it is doing....
The 'grep' is looking for: anything, followed by a the character '*',
followed by the string 'ECU' followed by a character '*' followed by

anything. Eg:

dfs*ECU* adfas would match

dfs "ECU" adfa would NOT match
dfs "ECU" adfa would NOT match
dfs ECU adf would NOT match

If all the files are in one directory,
grep "ECU" *

If you need to use 'find' (to recursively go down the directory
heirarchy) use:

Note: The "-type f" selects only 'regular' files (eg, not directories,
links, sockets, etc.) which cuts down on the amount of work the
"grep" does which can improve performance.

Note2: When a plus sign "+" is used, the -exec aggregates a set of
pathnames and executes on the set; when a semicolon ";" is used,
the -exec executes on one pathname at a time. The reason for
preferring + to a semicolon is vastly improved performance.
This is not supported on all versions of Unix.